More on B12 content in Tempeh, Seaweeds, Organic Produce, and Other Plant Foods, below…

Summary: No food in Europe or the U.S. other than Japanese Nori, has been tested* for lowering MMA levels (*at the time of publication of this original article).

Thus, the discussion about whether Western vegans can get B12 from plant foods can, and probably should, end here (until proper research is conducted). Because so many plant foods have failed other tests that do not measure up to the MMA lowering test, and because there are so many false rumors being passed around, the studies of B12 in plant foods are examined in detail below.

The only plant foods which have been tested for B12 activity using the gold standard of lowering MMA levels in humans are dried and raw nori from Japan. Dried nori made MMA status worse, indicating that it can reduce B12 status and can possibly harm people who are B12-deficient. Raw nori kept MMA levels about the same, indicating that it didn’t harm B12 status, but it did not help either.

Of all the foods studied below, only tempeh in Indonesia or Thailand, dulse, Chlorella, raw nori, Aphanizomenon flos-aquae, and coccolithophorid algae warrant much further attention for providing B12. Unless these foods are shown consistently to correct B12 deficiency, vegans should not rely on them as a B12 source.

It would be great to find a reliable plant source of B12 for vegans. One might get the opposite impression given my level of critique of some of these studies. My skepticism is only due to the potential harm from relying on a food that contains inactive B12 analogues which can make a B12 deficiency even worse.